1. Field of Technology
The present disclosure relates to a backlight unit and, more particularly, to a backlight unit capable of suppressing light leakage due to separation of a reflective sheet, and a liquid crystal display device including the same.
2. Background of the Related Art
A liquid crystal display (LCD) device is a light transmitting type display device which displays an image using optical properties of liquid crystal. Thus, the LCD device includes a backlight unit providing light to a liquid crystal panel. The backlight unit is classified into a direct type backlight unit and an edge type backlight unit depending on the position of the light source.
In order to enhance characteristics of light emitted from a light source, for example, luminance uniformity, maximum luminance, and the like, the backlight unit of the LCD device includes an optical sheet including a prism sheet, or the like.
FIG. 1 is a cross-sectional view of a related art LCD device.
As illustrated in FIG. 1, the related art LCD device includes a backlight unit 10 for providing light to a liquid crystal panel.
The backlight unit 10 includes a light source unit 5, a light guide plate 1, an optical sheet 6, and a reflective sheet 7.
The light source unit 5 includes a light source 2 and a circuit board 3. The light source 2 includes a plurality of light emitting diodes (LEDs), and the plurality of LEDs are arranged to be mounted on the circuit board 3.
The light guide plate 1 is disposed to be adjacent to the light source 2. The light guide plate 1 reflects the light output from the light source 2 to thus transfer and output such light via an upper surface thereof.
The optical sheet 6 is disposed on the light guide plate 1. The optical sheet 6 includes a prism sheet 6a and a protective sheet 6b. The prism sheet 6a collects light emitted from an upper surface of the light guide plate 1 and diffuses the collected light to provide the same to the liquid crystal panel. The protective sheet 6b is disposed between the prism sheet 6a and the light guide plate 1 to protect the prism sheet 6a from being damaged by the light guide plate 1.
The reflective sheet 7 is disposed on a rear surface of the light guide plate 1. The reflective sheet 7 reflects light leaked to the rear surface of the light guide plate 1 back to an upper surface of the light guide plate 1.
The light source unit 5, the light guide plate 1, the optical sheet 7, and the reflective sheet 6 are accommodated by a guide panel 8 and fixed therein. A light blocking tape 9 attached from a portion of an upper surface of the optical sheet to an upper end of a side wall of the guide panel 8, light output from the light source 2 is light shielded from being leaked to a region other than the liquid crystal panel.
Meanwhile, the optical sheet 6 of the backlight unit is formed by stacking two prism sheets in order to reduce the thickness of the backlight unit 10 and suppress generation of certain types of defects, such as creation of sheet creases and so-called Newton ring effects. Here, a space between the light blocking tape 9 and the light source 2 of the light source unit 5 is narrowed, and thus, a structure in which the circuit board 3 of the light source unit 5 is positioned on the rear surface of the light guide plate 1 is used.
Also, in the related art backlight unit 10, in order to additionally reduce the thickness, a container for accommodating the components of the backlight unit 10, for example, a bottom cover is omitted.
According to this structure, in the related art backlight unit 10, the reflective sheet 7 is attached to cover substantially the entire rear surface of the light guide plate 1 and a portion of a rear surface of the circuit board 3 of the light source unit 5, and a guide panel 8 supports both side portions of the reflective sheet 7.
Here, due to a difference between the thickness of the reflective sheet 7 and the thickness of the circuit board 3, a step A (or uneven portion) is formed when the reflective sheet 7 is attached. The step A may cause the reflective sheet 7 is being peeled-off (or separated) from the rear surface of the light guide plate 1, and the separation of the reflective sheet 7 causes certain problems, such as light leakage issues, displaying of dark spots, and the like, with respect to the backlight unit 10.